In the timeline of an universe (or, even more appropriately, a Multiverse), we're just as miniscule as the dinosaurs, and everything that we create will erode over time. A passersby 100,000,000 years from now may visit and, in the best outcome, may find us or descendants of us, but it is likely they will not find anything at all, 'cept maybe some ruins... and even those will have eroded and have been destroyed by then.
There's a TV program
"Life After People", which postulates that, if humans were to disappear from Earth for whatever reason (a hypothetical scenario, for the sake of simplicity, is that we just vanished for no reason) shows that it would take barely 500 years or so for nature to completely overshadow, erode, corrode, and destroy any semblance of our oh-so-mighty civilization. Even the satellites we have orbiting our planet would become nothing more than shooting stars, exploding and disintegrating as they plummet into our atmosphere.
So no, we're really not significant. Our human egotistical brain forces us to think we're hot shit (and, comparatively, right now we are, since there's no opposing might to our intellect and behavior anywhere we've looked), but our legacy is looking bleaker and bleaker as we continue to live in this planet and destroying it as a result. It will get the last laugh, eventually.
I'm in the camp that believes that in such a huge ocean of an universe, our solar system is but one tiny molecule in it. The chances of there being other life forms, with higher intelligence and more accomplishments done in their racial lifetime is likely to be far greater... but they would be too distant from us for us to have ever known them. Without the ability to travel great distances in a short time (which would require the bending of the laws of physics, a theme bordering more on science fiction than science fact, but not implausable or impossible given what little we know), it is unlikely that we will ever meet them. It is also unlikely that they would care to meet us. After all, they have their own problems.
I would imagine that if such races exist, their concern on an Universal Scale is the same as ours: When the planet is on its last legs, what will they be able to do, to survive? The sun's power is not infinite, plus any incoming big Solar Flare can potentially destroy us by the time we're even able to see it coming. An asteroid may show up any minute now, and we currently do not have the abilities to move it out of its trajectory. Those are the biggest threats to Human Existence right now. We've just been in a optimal position and have the laws of probability on our side, and have been quite fortunate.
It is possible that we're all just dust specs inside a collector's jar, too.
God? He may very well exist, and we're one of his pet project. We could be code in someone's computer program, a set of binomes in a giant mainframe (ha ha! Reboot). We could, however, be very small.
It's a big big universe, and we're all really puny,
we're just tiny little specks about the size of Mickey Rooney.
Then again maybe this 'deity' is just a scientist with 8 eyes who's made us in a giant pitri dish and is watching to see when we end up killing ourselves. All of these are perfectly plausable theories. We just don't know. And I really think we should stop kidding ourselves and thinking we're so high and mighty. Cockroaches and Rats may outlive us... and they can survive even cosmic collisions (well, maybe not the rats).
Ha ha! Existentialism.